Monday, February 27, 2017

Three centuries of Rheingau vintages — Schloss Johannisberg

The central German vineyard region of the Rheingau has a long history of active interest in vintage quality, as I have already discussed in the blog post The grand-daddy of all vintage charts. Individual vineyards within this region also have long records regarding their vintages, notably the three centuries of recording for Schloss Johannisberg. Finding this information online is not easy, and so I will
be covering it in this blog post.

This post follows my previous ones on individual producers, including century-long records from Piemonte, in northern Italy. for Fontanafredda; and Marchesi di Barolo.

Schloss Johannisberg is formally known as Fürst von Metternich-Winneburg'sche Domäne Schloss Johannisberg. You can read all about the estate and winery at the Johannisberg web site (in both English and German).

It is written in both German and English [German title: Schloss Johannisberg: Neun Jahrhunderte Weinkultur am Rhein]. The data (pp. 119-128) cover the vintages from 1700 to 2000 inclusive, and were compiled by Dr. h.c. Josef Staab.

For almost every vintage, the data consist of wine quantity, in hectoliters, and a brief verbal description of quality. Unfortunately, the verbal descriptions vary greatly across the three centuries, and so they are not directly comparable. I have therefore standardized them into a semi-quantitative score as follows:

Here is a summary of the harvest-quality data presented as a frequency histogram
of increasing quality. For random data his would follow what is known
as a binomial probability distribution. The graph approximately does so, but it
is slightly over-dispersed for a perfect fit (ie. not enough scores of
3, and too many 1, 5, 6).

In the next graph I have shown the harvest-quality data as a time series. Each data point represents one vintage, and the pink line is a running average (it shows the average value across groups of 9 consecutive years, thus smoothing out the long-term trends). [Technical note: the data are of ordinal type but not necessarily interval type, and so calculating an average may not actually be valid. I have simply assumed that it is appropriate, given the relatively close fit to the binomial probability distribution.]

Using the scale 0-6, the average vintage score is 3.2, whereas it would be c.3 for random data, so that the average harvest across the 301 years was slightly above expectation. There is no general long-term trend in vintage quality across these three centuries, as was also true for the Rheingau region in general (see The grand-daddy of all vintage charts). Nevertheless, Scores 1 and 2 do decrease in frequency from the 1940s onward — Score 1 occurs only in 1941, 1956 and 1965; and Score 2 occurs only in 1954, 1955, 1964 and 1984.

The next graph shows the frequency of the various starting dates for the grape harvest across the three centuries. It is worth pointing out that at Schloss Johannisberg harvest occurs several weeks after the rest of the Rheingau — this has been a deliberate strategy for a very long time, to get the grapes extra ripe.

There are actually some quite regular peaks and troughs in this graph. However, the most obvious point is the lack of harvests starting on November 1 at any time during the 301 years, which is compensated by an over-abundance of starts on November 2. Of course, All Saints' Day (or All Hallows' Day, Allerheiligen) falls on 1 November. This an optional holiday that is officially observed only in parts of Germany. Indeed, this day is a public holiday in the states of Baden-Württemberg, Bayern, Rheinland-Pfalz, Nordrhein-Westfalen and Saarland. However, the Rheingau is in the state of Hessen, instead, where November 1 is not an official holiday. So, everywhere else in the vineyard area along the Rhine and Mosel rivers All Saints' Day is an official holiday, but not here! That doesn't seem to have ever stopped the locals from taking a day off, though, does it?

The next graph shows the time course of the vintage start dates, with the dates simply numbered from 1 as the earliest observed date. Once again, the pink line is a running average. [Note that for some years an exact start date was not specified.]

These dates are spread across more than seven weeks, from earliest to latest. The latest dates occurred at the end of the 1800s, which was the end of the global cold period known as the Little Ice Age (1300-1850 CE). More importantly for modern global warming, the harvests have generally started earlier from the 1960s onwards. The last November harvest start was in 1955, and since 1965 there have been only two years when the harvest was started in the last week of October. The first September harvest start for three centuries occurred in 1976.

The final graph shows the time course of the vintage harvest quantity.

Obviously there is a sudden and inexorable increase in grape yield at the beginning of the 1930s. This does not appear to coincide with the purchase of extra land or any other increase in vineyard area. Indeed, I can find no mention of this change at all in the book from which the data come. However, Karl Storchmann (American Association of Wine Economists Working Paper No. 214. 2017) shows that the same trend applies to all of Germany; and he suggests "changes in production technologies or climatic conditions as potential drivers."

Finally, we could compare the harvest quality scores from this single vineyard with the quality scores for the Rheingau as a whole, as listed in the previous blog post (The grand-daddy of all vintage charts). Oddly, correlation analysis indicates that the relationship between these scores is extremely poor — only 12% of the variation in scores is related between the two datasets. That is, good years in the Rehingau as a whole are not necessarily good years for Schloss Johannisberg, and vice versa.

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About this blog

In the interests of doing something different to every other wine blogger, this blog will delve into the world of wine data, instead of wine itself. The intention is to ferret out some of the interesting stuff, and to bring it out into the light, for everyone to see. In particular, I will be drawing pictures of the data — as William Playfair said (in 1805): "whatever can be expressed in numbers may be represented by lines". Hopefully, this will be both interesting and informative.